Neutron Beam Reproducibility for the Accelerator-Based Boron Neutron Capture Therapy System Employing the Solid-State Lithium Target
Abstract
Purpose
Accelerator-based boron neutron capture therapy (BNCT) system employing a solid-state lithium target has been implemented into clinical practices. However, due to the degradation of the Li target over its lifetime, periodic replacement is necessary. This study aims to evaluate the reproducibility of neutron distribution for the accelerator-based BNCT system across different Li targets.
Methods
The system (CICS-1) was installed at the National Cancer Center Hospital, Tokyo, Japan, and used in this study. Depth and lateral thermal neutron distributions within PMMA phantoms were measured with four Li targets from different lot numbers in the accelerator-based BNCT system. These distributions were compared with the representative distributions for each Li target using the statistical analysis (Shapiro-Wilk, Bartlett, and One-Way analysis of variance tests). A p-value of less than 0.05 was considered statistically significant. Thermal neutrons were evaluated by saturated radioactivity of gold wire encapsulated with and without the cadmium capsule in each measurement position.
Results
Discrepancy (mean ± standard deviation) between the measured and representative depth thermal neutron distributions in the four Li targets followed a normal distribution (p = 0.10, 0.20, 0.72, and 0.30) and showed equal variance (p = 0.79), and was (-0.407±0.770), (-0.33±0.91), (0.883±0.721), and (-0.146±0.752)%, respectively. The discrepancy for the lateral distributions also followed a normal distribution (p = 0.39, 0.24, 0.98, and 0.51) and showed equal variance (p = 0.87), and was (-0.068±0.994), (-0.456±0.879), (0.582±0.878), and (-0.058±0.875)%, respectively. These discrepancies were within the measurement uncertainty of the thermal neutron flux (2.6%). Furthermore, these discrepancies had no statistical differences among the four Li targets (p = 1.00 (depth), 1.00 (lateral)).
Conclusion
This study demonstrates the neutron beam reproducibility in the accelerator-based BNCT employing the solid-state Li target. These findings are important for ensuring the stable dose delivery and contributing to robust quality assurance protocols in clinical practice.